1. Field of the Invention
The present invention relates to a removable core cylinder lock, comprising a cylinder lock casing having a casing wall defining an axially extending cavity with an insertion opening, a removable cylinder lock core which has an outer contour corresponding to the inner contour of said cavity and which is axially insertable into the cavity through the insertion opening. The lock core has an upper, substantially massive part with a row of holes for accommodating locking tumblers, and a lower part defining a cylindrical bore extending therethrough. A cylindrical, rotatable key plug is located in the cylindrical bore and has a longitudinal key slot for receiving a key co-operating with the locking tumblers, a retainer adapted to releasably retain the lock core in an inserted position in the cavity in the lock casing, and mutually fitting parts in the rear, axially inner portions of the casing and the lock core, including projections at the rear end portion of the casing and corresponding recesses at the rear end portion of the lock core.
2. Description of Related Prior Art
Such locks are previously known from commercial embodiments offered on the market by the Best Lock Company. In these embodiments, the projection at the rear end portion of the casing comprises a pair of relatively narrow pins on a rotatable locking member, whereas the corresponding recess comprises a corresponding pair of axial bores in the key plug.
However, in such a lock, including a casing and a lock core, it is quite possible to replace a lock core of a first kind by a lock core of a second kind provided that the replacing lock core has the same or a narrower outer contour and similar axial bores in the key plug.
The object of the present invention is to further develop such a lock so as to prevent such replacement of the lock core, or at least make such replacement more difficult.
According to the present invention, this object is achieved in that the projections of the casing comprise two lugs extending radially inwards from the casing wall on each side of a central vertical plane of the casing, in that the corresponding recesses comprise two recesses located in the massive part on both sides of a central rear portion containing the row of holes, the two recesses being dimensioned to accommodate two lugs, so as to permit full insertion of the lock core into the casing, and in that the two lugs are each provided with means for fastening the casing to an object.
With such a structure, a similar lock core with exactly the same outer contour and the same length cannot be inserted into the casing unless it is provided with the same kind of recesses at its rear portion. It is a very difficult matter to measure the dimension of the lugs at the innermost end of the casing and to make a corresponding recess in the lock core.
The two lugs are separated transversely from each other so as to leave a central passage therebetween. The central rear portion of the removable core fits into this central passage.
Also, the lugs at the rear portion of the casing are used to provide means for fastening the casing to an object, such as a door or the like. Thus, the fastening means are concealed behind the lock core itself, and it will be difficult to reach the fastening means from the outside by drilling or similar operations.
The lugs and the recesses should have a substantially supplementary configuration. Preferably, each lug is defined by a concave cylindrically curved surface, whereas the lug has a corresponding convex cylindrically curved surface.
Accordingly, the structural features of the casing and the lock core will enable easy insertion of a correctly designed lock core into the casing, whereas a similar lock core, having the same outer contour, the same length but no corresponding recess of the specific kind and dimensions, cannot be inserted into the casing. Moreover, it is difficult to provide such a recess in the similar lock core by straight forward machining operations. Therefore, the removable core cylinder lock according to the invention has a high degree of security against unauthorized manipulation of the lock by replacement of the lock core with a less secure lock core of another kind.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.